The formation of Australia's most powerful and militant union is a step closer, with delegates at the maritime union's national conference unanimously voting in favour to merge with the construction union.

The Maritime Union of Australia (MUA) and the Construction, Forestry, Mining and Energy Union (CFMEU) publicly floated the idea of a merger in October last year.

Key points:

MUA delegates vote in favour of proposal to merge with CFMEU

The proposal will now go to the CFMEU national executive who are expected to endorse the merger

On Monday, MUA delegates agreed to the proposal, which strongly condemned "the extreme political nature of the industrial offensive against Australian workers from neo-conservative commercial forces and the Abbott [now Turnbull] Government".

"The offensive includes the systematic destruction of Australian workers' rights and job security, particularly through industry policy that is destroying manufacturing and related service industries and, the systematic reduction of trade union rights in mining, hydrocarbon and construction industries in particular," the MUA's Principles for Amalgamation document stated.

"The Royal Commission into Trade Unions and the constant attempts to further erode worker protections and rights through new legislation and the revisiting of old legislation, like the ABCC, is central to this offensive."

MUA national secretary Paddy Crumlin has heralded the decision as a win for the union movement.

But Mr Crumlin said the merger would only go ahead if the MUA were able to keep its identity, and operate as a division of the much larger CFMEU.

"[Members] know that they're entering into a marriage, it's like any marriage, they want to keep their personality, they don't want it to be subsumed," Mr Crumlin said.

"There's a process of getting to that situation before marital vows are exchanged to ensure that we keep this great and long and proud history.

"We know we're entering into a marriage that's going to transform the ability of us to protect ourselves on the job, and in doing that transform the ability of other workers in that union to be able to protect themselves."

The proposal will now go to the CFMEU national executive, who are due to meet later this week and are expected to endorse the merger.

"I think our executive and our union will be looking forward to working with the MUA and the TCFUA [Textile, Clothing and Footwear Union of Australia] to create a new union which is looking after its members, looking after their families and looking after the communities that rely on their jobs," said Michael O'Connor, national secretary of the CFMEU.

"Those conditions that the MUA have put, I'm sure will be greeted positively by our executive.

"We'll take whatever time is necessary to get the new union structure right, to involve all our members, to make sure the process is transparent and democratic, because that's what we're all about."

If agreed to by the CFMEU, the plan will then go back to MUA members to finalise the deal.

"The fact that the two most militant unions in Australia are proposing to merge is extremely concerning," Senator Cash said.

"The potential merger of further unions to cover the majority of transport logistics across Australia should concern all Australians.

"Since Mr Shorten became Opposition Leader, we have seen the increasing influence of radical unions over Labor policy — one can only imagine how this control would be exacerbated by these proposed mergers."

Industrial relations a key issue heading into election year

Industrial relations will be a key issue heading further into this election year, and legislation to reintroduce the Australian Building and Construction Commission (ABCC) is being held out as a possible trigger for a double dissolution poll.

The merger discussions could be seen as laying the groundwork for a union-led campaign against the Coalition, with a combined war chest.

"There's is a feeling within the CFMEU and the MUA and the wider trade union movement, that trade unions are beginning to mobilise again against the tremendous political cynicism that's currently prevailing in the government of the day and the political atmosphere in this country," Mr Crumlin said.

"The whole position of combining resources, it's not money, there's no Trojan horse here, it's not about getting control of the Labor Party and breaking the law.

"The whole thing that's going on here is that people want to have a fair go, and they're willing to join together and join hands with each other to make sure that happens."

Whether TCFUA members will also form part of the united front, with its executive lobbying for similar conditions as the MUA deal, is yet to be finalised.

"You never take workers for granted, it's a decision of our members and we'll respect that decision," said Michelle O'Neill, national secretary of the TCFUA.

"They want to make sure it's a union that they can see themselves in, that they feel confident that they're represented in the union, that their leadership is there, that they're part of the decision making.

"Our union is not doing this because we have to do it, we're doing it because we want to do it, our union is smaller than it once was, but it is an effective union for its members."